62.3 CTS A GRADE RAINBOW OBSIDIUM SLAB [F5712 ]

Item Information

This is a piece we cut off a rough specimen at app 45 degree angle to expose the amazing patterns.Great cutting experience.We have taken the photo with the rough wet.

General

Category

Volcanic glass

Formula
(repeating unit)

70–75% SiO2,
plus MgO, Fe3O4

Identification

Color

Deep black or blackish green

Fracture

Conchoidal

Mohs scale hardness

5–6[1]

Luster

Vitreous

Specific gravity

~2.4[2]

Optical properties

Translucent

References

[3]

Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock.

It is produced when felsic lava extruded from a volcano cools rapidly with minimum crystal growth. Obsidian is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where the chemical composition (high silica content) induces a high viscosity and polymerization degree of the lava. The inhibition of atomic diffusion through this highly viscous and polymerized lava explains the lack of crystal growth. Obsidian is hard and brittle; it therefore fractures with very sharp edges, which were used in the past in cutting and piercing tools, and has been used experimentally as surgical scalpel blades. It may contain patterns of gas bubbles remaining from the lava flow, aligned along layers created as the molten rock was flowing before being cooled. These bubbles can produce interesting effects such as a golden sheen (sheen obsidian). An iridescent, rainbow-like sheen (rainbow obsidian) is caused by inclusions of magnetite nanoparticles